Fabrication of printed organic electronics (POE) is of profound interest, as such devices are ultra-low cost, are solution processable, and possess mechanical durability and structural flexibility. One type of POE, a printed thin-film transistor (TFT), has received much attention in recent years as it is a promising, low cost alternative to silicon technology for application in, for example, active-matrix liquid crystal displays (LCDs), organic light emitting diodes, e-paper, radio frequency identification tags (RFIDs), photovoltaics, and the like.
TFTs are generally composed of a supporting substrate, three electrically conductive electrodes (gate, source and drain electrodes), a channel semiconductor layer, and an electrically insulating gate dielectric layer separating the gate electrode from the semiconductor layer. It is desirable to improve the performance of known TFTs. Performance can be measured by at least two properties: mobility, and the on/off ratio. Mobility is measured in units of cm2/V·sec; higher mobility is desired. The on/off ratio is the ratio between the amount of current that leaks through the TFT in the off state versus the current that runs through the TFT in the on state. Typically, a higher on/off ratio is more desirable.
Organic thin-film transistors (OTFTs) can be used in applications such as radio frequency identification (RFID) tags and backplane switching circuits for displays, such as signage, readers, and liquid crystal displays, where high switching speeds and/or high density are not essential. They also have attractive mechanical properties such as being physically compact, lightweight, and flexible.
The semiconducting layers of OTFTs can be fabricated using low-cost solution-based patterning and deposition techniques, such as spin coating, solution casting, dip coating, stencil/screen printing, flexography, gravure, offset printing, ink jet-printing, micro-contact printing, and the like. To enable the use of these solution-based processes in fabricating thin-film transistor circuits, solution processable materials are therefore required. However, organic or polymeric semiconductors formed by solution processing tend to suffer from limited solubility, air sensitivity, and especially low field-effect mobility. This poor performance may be attributable to the poor film-forming nature of small molecules.
Despite the advances in the development of semiconducting polymers and related materials for use in photovoltaic devices, a need exists for materials and materials processing that (1) improve the performance of these devices, (2) maintain a good solubility in non-toxic solvents and (3) have a good environmental stability. The present application seeks to fulfill this need and provides further related advantages.